Apologies if these have already been picked up, but the following classic puzzles are exact duplicates:

15/06/05 and 01/08/05 (already noted in a previous post)
01/10/05 and 03/01/06
02/10/05 and 02/01/06
03/10/05 and 05/01/06
08/10/05 and 06/01/06
11/10/05 and 20/01/06
14/10/05 and 19/01/06
17/10/05 and 22/01/06
20/10/05 and 26/01/06
22/10/05 and 28/01/06
29/11/05 and 18/02/06

Not only can the numbers be reassigned, but any of top3 middle3 or bottom 3 rows can be juggled. same goes for columns, and finaly exactly the same goes for blocks of 3 for columns and rows and that makes 6 to power 8 multiplied by 8! different versions of the same puzzle

Even if my maths aren't quite right, (for instance a puzzle might have no 9's showing or have a starting symmetry), there are clearly very many variants of the same puzzle- But the differences are superficial, since the same techniques are needed to solve all those variants (I think)!

The number of valid Sudoku solution grids is 6,670,903,752,021,072,936,960. This number is equal to 9! × 722 × 27 × 27,704,267,971, the last factor of which is prime. When symmetries are taken into account, there are 5,472,730,538 solutions.

("Valid" means unique, a single solution.)

So there are 5.5 (American) billion Sudoku SOLUTIONS which are not symmetric with any other. Presumably, each of these solutions has many possible starting grids.